Halthorn, son of Halthelion, was born in the North-Downs, once the realm of the noble Men of Arnor. To the locals he is known as Greenhood, a mysterious but kind-hearted man. Although seldomly observed, he reveals himself when the need is dire and has become a beacon of hope for any common folk in danger.

Not long after his birth, a raiding party of Orcs from Angmar passed through the region and found his father's house. They showed no mercy, slaughtering everyone in their path. Before the Orcs were able to breach the door, his mother had hidden him in a safe place within the house. Alas, only a few moments later both his parents perished in battle against the merciless horde. Fortunately, they were unaware of the hidden infant and failed to burn down the house because of the heavy rain that night. The next day, a party of Elves heading for the refuge of Lin Giliath in Meluinen passed the house and searched for survivors. They discovered Halthorn, and took him along on their journey. A few weeks later he was brought to the valley of Imladris, and was raised there by his mentor Echmaethor, a renowned Knight of Rivendell. He was trained in close-combat, marksmanship, horsemanship, tracking, trap-laying, healing and many others. With far sight, he excelled at the bow. At age 20, he returned to the North-Downs to serve as a Ranger of the North, as his father once did.

Many years later, when he was a battle-hardened man worthy of the name of Dúnadan, the Grey Company was preparing to head south and Halthorn was ordered to gather a company of the scattered but ever watchful Rangers staying behind to stand against the armies of Angmar, invading from the North. He founded the Green Company, organising the Rangers to defend the lands of Eriador against the minions of Sauron in the wake of Halbarad and his chieftain Aragorn.